These days, an attractive-looking hairstyle is generally considered an indispensable part of a groomed appearance. In order to achieve such an attractive hairstyle, the hair is subjected to cosmetic treatment methods which range from washing by means of a shampoo to permanent re-shaping by means of chemical/thermal methods, or permanent oxidative color brightening. Time-limited durable direct dyes and oxidation dyes are available for dyeing hair. These hair dyes are generally applied to the hair in the form of liquid or foam preparations. When applying dye preparations, for example brushes or foam dispensers are used as auxiliary.
The foam dispensers include in particular pump sprays or aerosol sprays, with the help of which the cosmetic preparations are sprayed via a valve, either by means of mechanical force effect or with the help of a propellant. Both methods have obvious disadvantages. Whereas pump sprays are generally not suitable for a long-lasting uniform spray application of hair-cosmetic preparations, aerosol sprays are based on the use of propellants or gas propellants which, on the one hand, do not display any cosmetic effect and from which, on the other hand, when handled incorrectly, can put a user at risk.
Faced with this background, there is a requirement for alternative ways of spraying or foaming hair-cosmetic preparations. Flash evaporation has proved to be one such alternative spraying method. In this method, which is described for example in international patent application WO 200183071 A1 (Henkel), a liquid or pasty composition including a solvent is heated in a sealed space to a temperature which is above the flash point of the solvent, whereby an above-atmospheric pressure is produced in the composition. When depressurizing (throttling). the liquid vaporizes and can then be sprayed for example by means of a suitable nozzle.
Even if the flash evaporation is thus suitable in principle for spray application of hair-cosmetic preparations, at the same time not every hair-cosmetic preparation can be sprayed by means of a flash evaporation method. On the one hand this is due to the heating of the cosmetic preparation which is required for flash evaporation, and on the other hand the specifics of the spray created by flash evaporation, for example the size and density of the droplets created, in the spray.
Therefore, it is desirable to make available specific hair-cosmetic preparations for dyeing keratin-containing fibers, which preparations, because of their chemical and physical properties, are suitable for precise spray application by means of a device for flash evaporation. Furthermore, the preparations should be suitable for achieving a good cosmetic effect after application by means of a flash evaporation method. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with this background of the invention.